Plasma display panel drive method

ABSTRACT

A method of driving a plasma display panel including discharge cells, each at an intersection of a scan electrode and a sustain electrode, and a data electrode. One field period is divided into a plurality of sub-fields, each having an initializing period, writing period, and sustaining period. The sustaining period of at least one sub-field has a first sustaining period and a second sustaining period. In the first sustaining period, a transition period of a sustain pulse applied to the scan electrode is not temporally overlapped with a transition period of a sustain pulse applied to the sustain electrode. In a second sustaining period, a transition period of the sustain pulse applied to the scan electrode is temporally overlapped with a transition period of the sustain pulse applied to the sustain electrode. The second sustaining period is included at least at the end of the sustaining period.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is the National Stage of International Application No.PCT/JP2003/015856, filed Dec. 11, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of driving a plasma displaypanel used as a thin display device having a large screen and lightweight.

2. Description of the Related Art

An alternating current surface-discharging panel representing a plasmadisplay panel (hereinafter abbreviated as a panel) has a plurality ofdischarge cells formed between facing front and rear panels. In thefront panel, a plurality of display electrodes, each formed of a pair ofscan electrode and sustain electrode, are formed on a front glasssubstrate in parallel with each other. A dielectric layer and aprotective layer are formed to cover these display electrodes. On theother hand, in the rear panel, a plurality of data electrodes is formedin parallel with each other on a rear glass substrate. A dielectriclayer is formed on the data electrodes to cover them. Further, aplurality of barrier ribs are formed on the dielectric layer in parallelwith the data electrodes. Phosphor layers are formed on the surface ofthe dielectric layer and the side faces of the barrier ribs. Then, thefront panel and the rear panel are arranged to face each other and aresealed together so that the display electrodes and data electrodesintersect with each other and a discharge gas is filled into an internaldischarge space formed therebetween. A discharge cell is formed at apart where a display electrode is faced with a corresponding dataelectrode. In a panel structured as above, ultraviolet light isgenerated by gas discharge in each discharge cell. This ultravioletlight excites respective phosphors to emit R, G, or B color, for colordisplay.

A general method of driving a panel is a so-called sub-field method: onefield period is divided into a plurality of sub-fields and combinationof light-emitting sub-fields provides gradation images for display.Among such sub-field methods, a novel driving method of minimizing lightemission unrelated to gradation representation to improve a contrastratio is disclosed in Japanese Patent Unexamined Publication No.2000-242224.

FIG. 8 shows an example of driving waveforms of a conventional plasmadisplay panel with an improved contrast ratio. These driving waveformsare described hereinafter. One field period is composed of n sub-fields,each having an initializing period, writing period, and sustainingperiod. The sub-fields are abbreviated as a first SF, second SF, and soon to an n-th sub-field. As described below, in sub-fields except thefirst SF among these n sub-fields, initializing operation is performedonly on discharge cells that have been lit during the sustaining periodof the previous sub-field.

In the former half of the initializing period of the first SF,application of a gradually-increasing ramp voltage to scan electrodescauses weak discharge so that wall electric charge necessary for writingoperation is provided on each electrode. At this time, in order tooptimize the wall electric charge afterwards, excessive wall electriccharge is provided. In the following latter half of the initializingperiod, application of a gradually-decreasing ramp voltage to the scanelectrodes causes weak discharge again, to weaken the wall electriccharge excessively stored on each electrode and adjust the wall electriccharge to a value appropriate for each discharge cell.

In the writing period of the first SF, writing discharge is caused indischarge cells to be lit. In the sustaining period of the first SF,sustain pulses are applied to scan electrodes and sustain electrodes tocause sustaining discharge in the discharge cells in which writingdischarge has occurred. Thus, the phosphors of the correspondingdischarge cells emit light for image display.

In the following initializing period of the second SF, the same drivingwaveforms as the latter half of the initializing period of the first SF,i.e. a gradually-decreasing ramp voltage, is applied to the scanelectrodes. This is because the wall charge necessary for writingoperation is provided at the time of sustaining charge and thus theformer half of the initializing period need not be providedindependently. Therefore, weak discharge occurs in the discharge cellsin which sustaining discharge has occurred in the first SF, to weakenthe wall discharge excessively stored on each electrode and adjust thewall discharge to a value appropriate for each discharge cell. Indischarge cells in which no sustaining discharge has occurred, the wallcharge at the time of completion of the initializing period of the firstSF is maintained. Thus, discharge does not occur.

As described above, the initializing operation in the first SF is anall-cell initializing operation in which all the cells are discharged.The initializing operation in the second SF or after is a selectiveinitializing operation in which only discharge cells subjected tosustaining discharge are initialized. For this reason, light emissionunrelated to display is weak discharge occurring in the initializingoperation of the first SF only. Thus, images with high contrast can bedisplayed.

However, in spite of display of images with high contrast, the abovedriving method has a problem of increasing voltage applied to the dataelectrodes in order to ensure the wiring discharge.

The present invention addresses the above problem and aims to provide amethod of driving a plasma display panel capable of displaying imageswith high contrast without increasing the voltages applied to the dataelectrodes.

DISCLOSURE OF THE INVENTION

To attain the above object, a method of driving a plasma display panelof the present invention includes: dividing one field period into aplurality of sub-fields, each having an initializing period, writingperiod, and sustaining periods; and providing a first sustaining periodand a second sustaining period in a sustaining period of at least onesub-field. In the first sustaining period, a transition period ofsustain pulses applied to scan electrodes and a transition period ofsustain pulses applied to sustain electrodes are not temporallyoverlapped with each other. In the second sustaining period, atransition period of sustain pulses applied to the scan electrodes and atransition period of sustain pulses applied the sustain electrodes aretemporally overlapped with each other. The second sustaining period isincluded at least at the end of the sustaining period.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a part of a plasma displaypanel in accordance with an exemplary embodiment of the presentinvention.

FIG. 2 is a diagram illustrating an array of electrodes in the plasmadisplay panel.

FIG. 3 is a diagram illustrating a structure of a plasma display deviceusing a driving method in accordance with the exemplary embodiment ofthe present invention.

FIG. 4 shows an example of a driving circuit diagram for generatingsustain pulses in the plasma display device.

FIG. 5 is a diagram showing driving waveforms applied to respectiveelectrodes of a plasma display panel in accordance with the exemplaryembodiment of the present invention.

FIG. 6 is a diagram showing driving waveforms, light-emission waveforms,and control signal waveforms of switching elements in a sustainingperiod of the plasma display panel in accordance with the exemplaryembodiment of the present invention.

FIG. 7 is a diagram illustrating a structure of a plasma display devicefor changing duration of a second sustaining period according to apercentage of lit discharge cells in the exemplary embodiment of thepresent invention.

FIG. 8 is a diagram showing driving waveforms of a conventional plasmadisplay panel.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

An exemplary embodiment of the present invention is describedhereinafter with reference to the accompanying drawings.

FIG. 1 is a perspective view illustrating a part of a plasma displaypanel in accordance with the exemplary embodiment of the presentinvention. Panel 1 is composed of front substrate 2 and rear substrate 3that are made of glass and are arranged to face each other so as to forma discharge space therebetween. On front substrate 2, a plurality ofdisplay electrodes, each formed of a pair of scan electrode 4 andsustain electrode 5, is formed in parallel with each other. Dielectriclayer 6 is formed to cover scan electrodes 4 and sustain electrodes 5.On dielectric layer 6, protective layer 7 is formed. On the other hand,on rear substrate 3, a plurality of data electrodes 9 covered withinsulating layer 8 is provided. Barrier ribs 10 are provided oninsulating layer 8 between data electrodes 9 in parallel therewith.Also, phosphor 11 is provided on the surface of insulating layer 8 andthe side faces of barrier ribs 10. Front substrate 2 and rear substrate3 are arranged to face each other in a direction in which scanelectrodes 4 and sustain electrodes 5 intersect with data electrodes 9.In a discharge space formed therebetween, a mix gas, e.g. neon-xenon, isfilled as a discharge gas.

FIG. 2 is a diagram showing an array of electrodes on the panel. N scanelectrodes SCN 1 to SCNn (scan electrodes 4 in FIG. 1) and n sustainelectrodes SUS 1 to SUSn (sustain electrodes 5 in FIG. 1) arealternately disposed in a row direction. M data electrodes D1 to Dm(data electrodes 9 in FIG. 1) are disposed in a column direction. Adischarge cell is formed at a portion in which a pair of scan electrodeSCNi and sustain electrode SUSi (i=1 to n) intersects with one dataelectrode Dj (j=1 to m). Thus, m×n discharge cells are formed in thedischarge space.

FIG. 3 is a diagram illustrating a structure of a plasma display deviceusing a driving method of the exemplary embodiment of the presentinvention. The plasma display device includes panel 1, data drivercircuit 12, scan driver circuit 13, sustain driver circuit 14,timing-generating circuit 15, power supply circuits 16 and 17,analog-to-digital (A/D) converter 18, line number converter 19, andsub-field converter 20.

With reference to FIG. 3, video signal VD is fed into A/D converter 18.Horizontal synchronizing signal H and vertical synchronizing signal Vare fed into timing-generating circuit 15, A/D converter, line numberconverter 19, and sub-field converter 20. A/D converter 18 convertsvideo signal VD into image data of digital signals, and feeds thedigital image data into line number converter 19. Line number converter19 converts the image data into image data corresponding to the numberof pixels of panel 1, and feeds the image data to sub-field converter20. Sub-field converter 20 divides the image data of respective pixelsinto a plurality of bits corresponding to a plurality of sub-fields. Theimage data per sub-field is fed into data driver circuit 12. Data drivercircuit 12 converts the image data per sub-field into signalscorresponding to respective data electrodes D1 to Dm. Then, responsiveto the signals, data driver circuit 12 supplies voltages of power supplycircuit 16 to respective electrodes.

Timing-generating circuit 15 generates timing signals SC and SU based onhorizontal synchronizing signal H and vertical synchronizing signal V,and feeds the timing signals into scan driver circuit 13 and sustaindriver circuit 14, respectively. The scan driver circuit 13 and sustaindriver circuit 14 are connected to power supply circuit 17. Responsiveto timing signal SC, scan driver circuit 13 feeds driving waveforms intoscan electrodes SCN1 to SCNn. Responsive to timing signal SU, sustaindriver circuit 14 feeds driving waveforms into sustain electrodes SUS1to SUSn.

FIG. 4 shows an example of a driving circuit diagram for generatingsustain pulses in scan driver circuit 13 and sustain driver circuit 14.A description is provided of sustain pulse generating circuit 33 on ascan electrode side. Switching elements 25 and 27 apply voltagesdirectly to scan electrodes SCN1 to SCNn from power supply source Vm orGND. Capacitor C, coil L, switching elements 26 and 28, and diodes 21and 22 constitute a power recovering circuit for applying voltages toscan electrodes SCN1 to SCNn without power consumption by causing thecapacity of the scan electrodes and coil L to resonate. Diodes 21 and 22prevent current backflow. Switching elements 25 to 28 are turned on whenan input signal is at a high level.

Sustain pulse generating circuit 35 on a sustain electrode side works inthe same manner. In other words, switching elements 29 to 32 correspondto switching elements 25 to 28, and diodes 23 and 24 to diodes 21 and22, respectively. These components constitute a circuit for applyingvoltages to sustain electrodes SUS1 to SUSn. Sustain pulse generatingcircuit 33 on the scan electrode side is coupled to scan electrodes SCN1to SCNn on panel 1 via scan pulse generating circuit 34.

Next, a description is provided of driving waveforms for driving panel1. FIG. 5 is a diagram showing driving waveforms applied to respectiveelectrodes of a plasma display panel in accordance with the exemplaryembodiment of the present invention. The diagram shows driving waveformsfrom the first SF to the second SF.

In the initializing period of the first SF, while data electrodes D1 toDm and sustain electrodes SUS1 to SUSn are kept at 0V, a ramp voltagegradually increasing from voltage Vp (V) not higher than adischarge-starting voltage to voltage Vr (V) exceeding thedischarge-starting voltage is applied to scan electrodes SCN1 to SCNn.This causes a first weak initializing discharge in all the dischargecells. Thus, negative wall voltage accumulates on scan electrodes SCN1to SCNn and positive wall voltage accumulates on sustain electrodes SUS1to SUSn and data electrodes D1 to Dm. Now, the wall voltage onelectrodes indicates a voltage generated by wall electric charge thataccumulates on the dielectric layer or phosphor layer covering theelectrodes.

Thereafter, sustain electrodes SUS1 to SUSn are kept at positive voltageVh (V), and a ramp voltage gradually decreasing from voltage Vg (V) tovoltage Va(V) is applied to scan electrodes SCN1 to SCNn. This causes asecond weak initializing discharge in all the discharge cells. The wallvoltage on scan electrodes SCN1 to SCNn and the wall voltage on sustainelectrodes SUS1 to SUSn are weakened, and the wall voltage on dataelectrodes D1 to Dm are adjusted to a value appropriate for writingoperation.

In this manner, in the initializing period of the first SF, all-cellinitializing operation in which initializing discharge occurs in all thedischarge cells is performed.

In the writing period of the first SF, scan electrodes SCN1 to SCNn areheld at voltage Vs (V) once. Next, positive write pulse voltage Vw (V)is applied to data electrode Dk of discharge cells to be lit in thefirst row among data electrodes D1 to Dm, and scan pulse voltage Vb (V)is applied to scan electrode SCN1 in the first row. At this time, thevoltage at the intersection between data electrode Dk and scan electrodeSCN1 totally amounts to the value in which the wall voltage on dataelectrode Dk and the wall voltage on scan electrode SCN1 are added tovoltage Vw-Vb applied from outside, thus exceeding thedischarge-starting voltage. This causes writing discharge between dataelectrode Dk and scan electrode SCN1, and between sustain electrode SUS1and scan electrode SCN1. Thus, positive wall voltage accumulates on scanelectrode SCN1, negative wall voltage accumulates on sustain electrodeSUS1, and negative wall voltage also accumulates on data electrode Dk inthis discharge cell. Thus, writing operation in which writing dischargeoccurs in the discharge cells to be lit in the first row to accumulatewall voltage on respective electrodes is performed.

On the other hand, the intersection of a data electrode to whichpositive write pulse voltage Vw (V) is not applied, and scan electrodeSCN1 does not exceed the discharge-starting voltage. Thus no writingdischarge occurs in this intersection.

Such writing operation is sequentially performed on the cells in thesecond row to the n-th row, and the writing period is completed.

In the sustaining period of the first SF, first, sustain electrodes SUS1to SUSn are reset to 0V, and positive sustain pulse voltage Vm (V) isapplied to scan electrodes SCN1 to SCNn. At this time, in the dischargecells in which writing discharge has occurred, the voltage across scanelectrode SCNi and sustain electrode SUSi amounts to addition of sustainpulse voltage Vm (V) and the wall voltage on scan electrode SCNi andsustain electrode SUSi, thus exceeding the discharge-starting voltage.This causes sustaining discharge between scan electrode SCNi and sustainelectrode SUSi. Thus, negative wall voltage accumulates on scanelectrode SCNi, positive wall voltage accumulates on sustain electrodeSUSi. At this time, positive wall voltage also accumulates on dataelectrode Dk.

Successively, scan electrodes SCN1 to SCNn are reset to 0V, and positivesustain pulse voltage Vm (V) is applied to sustain electrodes SUS1 toSUSn. In the discharge cells in which sustaining discharge has occurred,the voltage across sustain electrode SUSi and scan electrode SCNiexceeds the discharge-starting voltage. This causes sustaining dischargebetween sustain electrode SUSi and scan electrode SCNi again. Thus,negative wall voltage accumulates on sustain electrode SUSi, positivewall voltage accumulates on scan electrode SCNi.

Applying sustain pulse alternately to scan electrodes SCN1 to SCNn andsustain electrodes SUS1 to SUSn in a similar manner can continuesustaining discharge. Incidentally, in the discharge cells in which nowriting discharge has occurred in the writing period, no sustainingdischarge occurs, and a state of the wall voltage at the time ofcompletion of the initializing period is maintained. Thus, sustainingoperation in the sustaining period is completed.

As shown in FIG. 5, the sustaining period is composed of a firstsustaining period and a second sustaining period. This is a point of thepresent invention, and thus detailed afterwards.

Next, in the initializing period of the second SF, sustain electrodesSUS1 to SUSn are kept at voltage Vh (V), data electrodes D1 to Dm arekept at 0V, and a ramp voltage gradually decreasing from voltage Vm (V)to voltage Va(V) is applied to scan electrodes SCN1 to SCNn. This causesweak initializing discharge in the discharge cells in which sustainingdischarge has occurred in the sustaining period of the first SF. Thewall voltage on scan electrode SCNi and the wall voltage on sustainelectrode SUSi are weakened, and the wall voltage on data electrode Dkare adjusted to a value appropriate for writing operation. On the otherhand, in the discharge cells in which writing discharge or sustainingdischarge has not occurred in the first SF, no discharge occurs and astate of the wall charge at the time of completion of the initializingperiod of the first SF is maintained. In this manner, in theinitializing period of the second SF, selective initializing operationin which initializing discharge occurs in the discharge cells subjectedto sustaining discharge in the first SF is performed.

The writing period and sustaining period of the second SF are the sameas those of the first SF. Those of the third SF or after are the same asthose of the second SF. Thus, the description is omitted. Desirably, therelative voltage change of the ramp voltage in the initializing periodis up to 10 V/μs. In this embodiment, the relative voltage change is setto 2 to 3 V/μs, Va=−80V, Vh=150V, and Vm=170V.

Next, driving waveforms in the sustaining period are detailed. FIG. 6 isan enlarged diagram showing driving waveforms applied to scan electrodeSCNi and sustain electrode SUSi in the sustaining period, i.e. sustainpulses, and a waveform of light emitted with the sustain pulses.Additionally, signals for controlling switching elements 25 to 32 ofFIG. 4 are also shown as signals S25 to S32, respectively. As shown inthe diagram, each of the sustain pulses applied to scan electrode SCNior sustain electrode SUSi has a transition period (leading edge period)during which the sustain pulse changes from 0V to voltage Vm (V), a highperiod during which the sustain pulse is fixed at Vm (V), a transitionperiod (trailing edge period) during which the sustain pulse changesfrom Vm (V) to 0V, and a low period during which the sustain pulse isfixed at 0V. In the description of a sustain pulse applied to scanelectrode SCNi as an example, switching element 26 of FIG. 4 is turnedon by setting signal S26 at a high level in the leading edge period.Electric charge accumulated in capacitor C for power recovering issupplied to scan electrode SCNi via coil L to increase the voltage onscan electrode SCNi. Next, in the high period, signal S25 at a highlevel turns on switching element 25, voltage Vm (V) of a power supply ofVm (V) is supplied to scan electrode SCNi, and the voltage of scanelectrode SCNi is fixed to Vm (V). Next, in the trailing edge period,signals S25 and S26 at a low level and then signal S28 at a high levelturns on switching element 28. Thus, the electric charge accumulated onscan electrode SCNi is recovered into capacitor C for power recoveringvia coil L, and the voltage of scan electrode SCNi decreases. Next, inthe low period, signal S27 at a high level turns on switching element27, thus grounding scan electrode SCNi and fixing to 0V. The sameoperation applies to sustain electrode SUSi.

The sustaining period is composed of the first sustaining period and thesecond sustaining period as shown in FIG. 5. The detailed drivingwaveforms from the first sustaining period to the second sustainingperiod are shown in FIG. 6. With reference to FIG. 6, when sustainpulses are alternately applied to scan electrode SCNi and sustainelectrode SUSi, in the first sustaining period, the transition period ofa sustain pulse applied to scan electrode SCNi and the transition periodof a sustain pulse applied to sustain electrode SUSi are not overlappedwith each other. In the second sustaining period, the transition periodof the sustain pulse applied to scan electrode SCNi and the transitionperiod of the sustain pulse applied to sustain electrode SUSi are atleast partially overlapped with each other temporally. Specifically, inthe first sustaining period, after one of the display electrodes (e.g.scan electrode SCNi) is fixed at 0V, application of voltage to the otherof the display electrodes (e.g. sustain electrode SUSi) starts. However,in the second sustaining period, sustain pulses are applied so that thetrailing edge period of a pulse applied to one of the display electrodes(e.g. scan electrode SCNi) is overlapped with the leading edge period ofa pulse applied to the other of the display electrodes (e.g. sustainelectrode SUSi).

As described above, the method of driving a panel in accordance with thepresent invention has two sustaining periods: a first sustaining periodin which the transition period of a sustain pulse applied to scanelectrode SCNi is not temporally overlapped with the transition periodof a sustain pulse applied to sustain electrode SUSi; and a secondsustaining period in which the transition period of the sustain pulseapplied to scan electrode SCNi is temporally overlapped with thetransition period of the sustain pulse applied to sustain electrodeSUSi. The second sustaining period is included at the end of thesustaining period. This structure stabilizes the following initializingoperation, especially selective initializing operation, and ensureswiring operation without increasing voltages applied to data electrodes.

The reason why disposing the second sustaining period at least at theend of sustaining period stabilizes initializing discharge has notcompletely been elucidated; however, the following reasons areconsidered.

When we focus on the sustaining discharge, as shown in FIG. 6, thewaveform of light emission and the timing thereof are largely differentbetween the first sustaining period and the second sustaining period. Inthe first sustaining period, in discharge cells in which sustainingdischarge occurs, self-erase discharge d2 occurs time Tw (μs) after oneof the display electrodes (e.g. scan electrode SCNi) is fixed at 0V.Then, when application of voltage to the other of the display electrodes(e.g. sustain electrode SUSi) starts, major discharge d1 occurs. Incontrast, in the second sustaining period, major discharge d3 occurssubstantially without occurrence of self-erase discharge. Majordischarge d3 at this time is larger than major discharge d1 in the firstsustaining period.

The reason is described as follows. In the first sustaining period,first, the driving waveform of a pulse applied to one of the displayelectrodes (e.g. scan electrode SCNi) is lowered from Vm (V) to 0V. Thisgenerates self-erase discharge d2, and this self-erase dischargedecreases the wall charge accumulated on respective electrodes. Then,major discharge d1 occurs when voltage Vm (V) is applied to the other ofthe display electrodes (e.g. sustain electrode SUSi). However, at thistime, because of the lack of the wall voltage, major discharge d1 itselfis weakened. In contrast, in the second sustaining period, while thedriving waveform of the pulse applied to one of the display electrodes(e.g. scan electrode SCNi) goes down, the driving waveform of the pulseapplied to the other of the display electrodes (e.g. sustain electrodeSUSi) goes up. This causes major discharge d3 when or before theself-erase discharge occurs. Thus, with sufficient wall voltageaccumulated, major discharge d3 occurs. Therefore, major discharge d3 islarger than major discharge d1.

Based on this idea, the second sustaining period is included at least atthe end of the sustaining period. This can accumulate sufficientnegative wall voltage on scan electrode SCNi and sufficient positivewall voltage on sustain electrode SUSi and data electrode Dk in adischarge cell in which sustaining discharge has occurred. For thisreason, application of a ramp voltage gradually decreasing from voltageVm (V) to Va (V) to scan electrode SCNi in the selective initializingoperation of the following sub-field can generate stable weak dischargebetween sustain electrode SUSi and scan electrode SCNi, and dataelectrode Dk and scan electrode SCNi. This weakens the wall voltage onscan electrode SCNi, the wall voltage on sustain electrode SUSi, and thewall voltage on data electrode Dk, thus adjusting the wall voltage to avalue appropriate for writing operation. Therefore, writing voltagenecessary for the following writing operation can be reduced and stableimage display can be assured.

However, for the conventional driving method, the sustaining period iscompleted in the first sustaining period. Thus, the sustaining dischargeis only weak major discharge d1. For this reason, negative wall voltageon scan electrode SCNi, and positive wall voltage on sustain electrodeSUSi and data electrode Dk are insufficient. This causes wall chargeincomplete for writing operation, such as no initializing discharge, andinsufficient charge adjustment even at occurrence of initializingdischarge in the initializing period of the following SF. To ensureoccurrence of writing discharge, insufficient wall voltage should becompensated. For this reason, higher voltage should be applied to dataelectrodes.

In a method of driving a panel of the present invention, including thesecond sustaining period at least at the end of the sustaining periodstabilizes the following initializing operation, especially selectiveinitializing operation, and forms wall charge appropriate for writingoperation. Incidentally, when the second sustaining period is lengthenedto increase the number of sustain pulses in which the transition periodsof waveforms applied to scan electrode and sustain electrode aretemporally overlapped, the following selective initializing operationcan be stabilized. However, when the number of pulses to be temporallyoverlapped increases to a certain degree, the effect is almost the same.The number of sustain pulses temporally overlapped that are necessaryfor stabilizing the initializing operation is influenced by a percentageof lit cells in a panel.

Now, in the driving waveforms in the second sustaining period, thetransition periods of the pulses applied to scan electrode SCNi andsustain electrode SUSi are temporally overlapped. For this reason, thepeak current flowing at charge/discharge of the electrodes is largerthan that of the driving waveforms in the first sustaining period. Thus,the power consumed in the resistance of the panel and circuits arelarger and reactive power tends to increase. Therefore, it is desirableto minimize the duration of the second sustaining period. For a drivingmethod of the present invention, in a panel 42 in. in diagonal, settingthe duration of the second sustaining period so that it includes approx.5 sustain pulses can stabilize the selective initializing operation.This can inhibit the increase in reactive power within a small range.

To further inhibit the increase in reactive power, a plasma displaypanel can be structured so that the duration of the second sustainingperiod is changed according to the percentage of lit discharge cells.

FIG. 7 shows a structure of a plasma display device for changing theduration of the second sustaining period according to the percentage oflit discharge cells. In addition to the structure of a plasma displaydevice shown in FIG. 3, means for detecting a percentage of litdischarge cells 40 is provided. Means for detecting a percentage of litdischarge cells 40 detects a percentage of lit discharge cells withrespect to all the discharge cells in each sub-field, according to thedata from sub-field converter 20. The percentage of lit cells in eachsub-field detected by means for detecting a percentage of lit dischargecells 40 is sent to timing-generating circuit 15. Timing-generatingcircuit 15 determines the duration of the second sustaining periodaccording to the percentage of lit cells, and controls scan drivercircuit 13 and sustain driver circuit 14.

When the percentage of lit discharge cells is small, current flowingthrough panel 1 and thus voltage drop are small. For this reason,voltage applied to each discharge cell is larger and causes strongdischarge. Therefore, because the amount of wall charge provided by thesustaining discharge is relatively large, the following initializingoperation can be stabilized even with a small number of sustain pulsestemporally overlapped. In contrast, when the percentage of lit dischargecells is large, current flowing through panel 1 and thus voltage dropare large. For this reason, voltage applied to each discharge cell issmaller and causes weak discharge. Therefore, because the amount of wallcharge provided by the sustaining discharge is smaller, the number ofpulses temporally overlapped must be increased. Thus, when thepercentage of lit discharge cells is small, the second sustain period isshortened. When the percentage of lit discharge cells is large, thesecond sustain period is lengthened. Such a change in the duration ofthe second sustain period according to the percentage of lit dischargecells can stabilize the initializing operation while minimizing anincrease in reactive power.

In FIG. 6, in the second sustaining period, the leading edge period of asustain pulse applied to one of electrodes (e.g. scan electrode SCNi) isexactly overlapped with the trailing edge period of a sustain pulseapplied to the other of the electrodes (e.g. sustain electrode SUSi).However, exact overlapping is not necessarily required. The duration, orperiod, during which the transition periods of sustain pulses areoverlapped with each other in the second sustain period can be set sothat a self-erase discharge substantially does not occur.

In the waveforms of FIG. 6, the entire transition periods of a sustainpulse applied to one of the display electrodes are disposed within thelow period of a sustain pulse applied to the other of the displayelectrodes. However, the entire transition periods of the sustain pulseapplied to one of the display electrodes can be disposed within the highperiod of the sustain pulse applied to the other of the displayelectrode.

In this embodiment, a ramp voltage waveform is used as a drivingwaveform for causing an initializing discharge in the initializingperiod. Instead of this ramp voltage waveform, a voltage waveform gentlychanging with a relative voltage change up to 10V/μs can be used.However, because too small relative voltage change lengthens theinitializing period and makes gradation representation difficult, thelower limit of the relative voltage change is set within a range inwhich a desired gradation representation is possible.

Further, in this embodiment, because initializing discharge occurs inall the cells irrelevant to the state of wall charge in respectivedischarge cells, in the first SF, the sustaining period of the sub-filedjust before the first SF (the last sub-field in one field period) neednot have the second sustain period.

As obvious from the above description, a method of driving a plasmadisplay panel of the present invention can cause a stable initializingdischarge and display images with high contrast without applying highvoltage to data electrodes thereof.

1. A method of driving a plasma display panel including a plurality ofdischarge cells, each discharge cell being formed at an intersection ofa scan electrode and a sustain electrode, and a data electrode, themethod comprising: dividing one field period into a plurality ofsub-fields, each comprising an initializing period, a writing period,and a sustaining period; providing a first sustaining period and asecond sustaining period in a sustaining period of at least onesub-field, in the first sustaining period, a transition period of asustain pulse applied to the scan electrode not being temporallyoverlapped with a transition period of a sustain pulse applied to thesustain electrode, and in the second sustaining period, the transitionperiod of the sustain pulse applied to the scan electrode beingtemporally overlapped with the transition period of the sustain pulseapplied to the sustain electrode; and disposing the second sustainingperiod at least at an end of the sustaining period, wherein, theduration of the second sustaining period is changed according to apercentage of lit discharge cells.